The Duchess of Cambridge’s hospitalization for morning sickness highlights the violent body reactions sometimes spurred by pregnancy — even a royal one. That may not be such a bad thing.

Morning sickness, when it’s not debilitating, is associated with positive pregnancy outcomes, said Samuel Flaxman, an evolutionary biologist at the University of Colorado in Boulder, who has studied the adaptive significance of the condition.

“There’s a robust relationship showing that women who have nausea and vomiting in pregnancy are less likely to miscarry than women without it,” Flaxman said in a telephone interview. “The hypothesis best supported to explain that is nausea and vomiting basically cause women to avoid foods that might have potentially harmful things in them.”

The duchess, the former Kate Middleton, was admitted to London’s King Edward VII Hospital with hyperemesis gravidarum, an extreme form of morning sickness, her office said Monday. Pregnancy triggers such severe nausea in as many as 2 percent of women that it prevents food and liquids from being kept down, threatening weight loss and dehydration, said Diana Ramos, assistant professor of obstetrics and gynecology at the University of Southern California’s Keck School of Medicine.

“She will be sent home with medication to prevent the nausea and vomiting, and encouraged to have lots of small meals high in protein and carbohydrates and low in fat,” said Ramos, who has no direct knowledge of the case. “Kate shows us that we are all human and subject to the same bodily functions.”

As many as 85 percent of women may experience nausea with or without vomiting during pregnancy, according to Ramos. Morning sickness usually occurs in the first months of pregnancy and ends by the fourth month, she said, adding that the name can be misleading because it can strike at any time.

One in five women may experience nausea and vomiting in pregnancy beyond the first trimester, according to Motherisk, a health promotion program run from Toronto’s Hospital for Sick Children whose telephone helpline receives about 40,000 calls a year. For an unfortunate minority, symptoms may persist until delivery.

“The cause of the morning sickness is uncertain, but an increase in certain hormone levels is believed to play a role,” Ramos said. “Other theories include a psychological predisposition and evolutionary adaptation.”

At least three studies in Canada, the United States and Italy are investigating new medications for relieving symptoms.

Of course, just because something makes a pregnant woman sick does not mean it is a threat, Flaxman said. It indicates instead that there may be an evolutionary reason why the steak a woman once loved turns her stomach during pregnancy.

“The kinds of things that tend to provoke nausea and vomiting are the kinds of things that, through evolutionary history, have been associated with ingesting toxins or food- borne microbes,” Flaxman said. “These are threats we all face when we eat, but the magnitude of the threat is increased during pregnancy.”

A heightened sense of smell during pregnancy is also connected with nausea and vomiting, Flaxman said. Some therapists suggest pregnant women remove everything “smelly” from their house to avoid feeling ill.

Miriam Erick, senior nutritionist at Brigham & Women’s Hospital in Boston, said a pregnant women’s heightened sense of smell is linked to an increase in the hormone estrogen.

“A lot of women have the radar nose of pregnancy,” said Erick, who has been researching morning sickness for more than 20 years and started the morning sickness nutrition clinic at Brigham & Women’s. “Estrogen is what drives a sense of smell. It really sends them over the edge.”

Many aspects of morning sickness are not well understood, including a correlation between increased nausea and vomiting and the likelihood a woman is carrying twins, Flaxman said.

“That’s one of those cases where we don’t know why that’s happening,” he said.

The duchess’s rare, severe form of sickness has ties to literary history. English writer Charlotte Bronte, author of the Victorian novel “Jane Eyre,” died in 1855 from what is thought to have been hyperemesis gravidarum.

“Today, women don’t die from it,” Erick said. “We have interventions, intravenous fluids and nutrition. We can do a fair amount of intervention, not that it would take away the nausea and vomiting.”

The safest and most reliable treatment for morning sickness is Diclectin, made by Blainville, Quebec-based Duchesnay, said Gideon Koren, a pediatric pharmacologist at the Hospital for Sick Children, who has been studying the safety of drugs in pregnancy for decades.

“It’s very safe based on studies with in excess of 250,000 women,” Koren said in an interview. “In Canada, it’s the drug of choice for morning sickness.”

GlaxoSmithKline’s Zofran, known to cause heart-beat irregularities when administered intravenously, and clonidine, a medication for anxiety and panic disorder whose impact on unborn babies isn’t yet understood, are also being studied, Koren said.

Treatment for morning sickness typically includes intravenous fluids for hydration, electrolyte supplements, medications to control vomiting, and the introduction of a diet of crackers and broth, said Ramos at the University of Southern California.